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Method Not Found

I’m trying to check if an Item exists via an HTTP GET to a frappe method. I am getting “Method Not Found”. I’m testing in Postman. /api/resource GETs are working fine.
I really need to use the frappe.db.exists() method to confirm if an Item Name (or Item Code) already exists.
I’ve tried a number of variations of the following:

GET ‘Item’, ‘AAAAA’) where ‘AAAAA’ is the item name to check
I appreciate any guidance